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Network Working Group S. Sun
Request for Comments: 3650 L. Lannom
Category: Informational B. Boesch
CNRI
November 2003
Handle System Overview
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
IESG Note
Several groups within the IETF and IRTF have discussed the Handle
System and its relationship to existing systems of identifiers. The
IESG wishes to point out that these discussions have not resulted in
IETF consensus on the described Handle System, nor on how it might
fit into the IETF architecture for identifiers. Though there has
been discussion of handles as a form of URI, specifically as a URN,
these documents describe an alternate view of how namespaces and
identifiers might work on the Internet and include characterizations
of existing systems which may not match the IETF consensus view.
Abstract
This document provides an overview of the Handle System in terms of
its namespace and service architecture, as well as its relationship
to other Internet services such as DNS, LDAP/X.500, and URNs. The
Handle System is a general-purpose global name service that allows
secured name resolution and administration over networks such as the
Internet. The Handle System manages handles, which are unique names
for digital objects and other Internet resources.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivations. . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Handle Namespace . . . . . . . . . . . . . . . . . . . . . . . 7
4. Handle System Architecture . . . . . . . . . . . . . . . . . . 8
5. Handle System Security . . . . . . . . . . . . . . . . . . . . 11
6. The Handle System and other Internet Services. . . . . . . . . 12
6.1. Domain Name Service (DNS). . . . . . . . . . . . . . . . 13
6.2. Directory Services (X.500/LDAP). . . . . . . . . . . . . 13
6.3. Uniform Resource Identifier (URI)/Uniform Resource Name
(URN). . . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations. . . . . . . . . . . . . . . . . . . . 15
7.1. General Security Practice. . . . . . . . . . . . . . . . 15
7.2. Privacy Protection . . . . . . . . . . . . . . . . . . . 16
7.3. Caching and Proxy Servers. . . . . . . . . . . . . . . . 16
7.4. Mirroring. . . . . . . . . . . . . . . . . . . . . . . . 17
7.5. Denial of Service (DoS). . . . . . . . . . . . . . . . . 17
8. History of the Handle System . . . . . . . . . . . . . . . . . 18
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
10. References and Bibliography. . . . . . . . . . . . . . . . . . 19
11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 21
1. Introduction
This document provides an overview of the Handle System, a
distributed information system designed to provide an efficient,
extensible, and secured global name service for use on networks such
as the Internet. The Handle System includes an open protocol, a
namespace, and a reference implementation of the protocol. The
protocol enables a distributed computer system to store names, or
handles, of digital resources and resolve those handles into the
information necessary to locate, access, and otherwise make use of
the resources. These associated values can be changed as needed to
reflect the current state of the identified resource without changing
the handle. This allows the name of the item to persist over changes
of location and other current state information. Each handle may
have its own administrator(s) and administration can be done in a
distributed environment. The Handle System supports secured handle
resolution. Security services such as data confidentiality, data
integrity, and non-repudiation are provided upon client request.
The Handle System provides a confederated name service that allows
any existing local namespace to join the global handle namespace by
obtaining a unique Handle System naming authority. Local names and
their value-binding(s) remains intact after joining the Handle
System. Any handle request to the local namespace may be processed
by a service interface speaking the Handle System protocol. Combined
with the unique naming authority, any local name is guaranteed unique
under the global handle namespace.
There are several services used today to provide name service for
Internet resources. Among these, the Domain Name System (DNS) [2,3]
is the most widely used. DNS is designed "to provide a mechanism for
naming resources in such a way that the names are mappable into IP
addresses and are usable in different hosts, networks, protocol
families, internets, and administrative organizations" [3]. The
growth of the Internet has raised demands for various extensions to
DNS. There are also attempts to use DNS as a general-purpose
resource naming system. However, the importance of DNS in basic
network routing has led to great caution in implementing any DNS
extension or overloading the DNS for general-purpose resource naming.
An additional factor which argues against using DNS as a general-
purpose naming service is the DNS administrative model. DNS names
are typically managed by the network administrator(s) at the DNS zone
level. There is no provision for per-name administrative structure
and no facilities for anyone other than the network administrator to
create or manage DNS names. This is appropriate for domain name
administration, but less so for general-purpose resource naming.
The Handle System has been designed from the start to serve as a
general-purpose naming service. It is designed to accommodate very
large numbers of entities and to allow distributed administration
over the public Internet. The Handle System data model allows access
control to be defined at the level of each of the data values
associated with a given handle. Each handle can further define its
own set of administrators that are independent from the network or
host administrator.
Traditional URLs (Uniform Resource Locators) [4] allow certain
Internet resources to be named as a combination of a DNS name and
local name. The local name may be a local file path, or a reference
to some local service (e.g., a cgi-bin script). This combination of
a DNS name and a local name provides a flexible administrative model
for naming and managing individual Internet resources. However, the
URL practice also has some key limitations. Most URL schemes (e.g.,
http) are defined for resolution only. Any URL administration has to
be done either at the local host, or via some other network service
such as NFS. Using a URL as a name typically ties the Internet
resource to its current network location. For example, a URL will be
tied to its local file path when the file path is part of the URL.
When the resource moves from one location to another for whatever
reason, the URL breaks. It is especially difficult to work around
this problem when the reason for the location change is change in
ownership of an asset, as ownership is generally reflected in the
domain name.
The Handle System is designed to overcome these limitations and to
add significant functionality. Specifically, the Handle System is
designed with the following objectives:
- Uniqueness: Every handle is globally unique within the Handle
System.
- Persistence: Handles may be used as persistent identifiers for
Internet resources. A handle does not have to be derived from
the entity that it names. While an existing name, or even a
mnemonic, may be included in a handle for convenience, the only
operational connection between a handle and the entity it names
is maintained within the Handle System. This of course does
not guarantee persistence, which is a function of
administrative care. But it does allow the same name to
persist over changes of location, ownership, and other state
conditions. For example, when a named resource moves from one
location to another, the handle may be kept valid by updating
its value in the Handle System to reflect the new location.
- Multiple Instances: A single handle can refer to multiple
instances of a resource, at different and possibly changing
locations in a network. Applications can take advantage of
this to increase performance and reliability. For example, a
network service may define multiple entry points for its
service with a single handle so as to distribute the service
load.
- Multiple Attributes: A single handle can refer to multiple
attributes of a resource, including associated services,
available through any method at different and possibly changing
network locations. Handles can thus be used as persistent
entry points into an evolving world of services associated with
identified resources.
- Extensible Namespace: Existing local namespaces may join the
handle namespace by acquiring a unique handle naming authority.
This allows local namespaces to be introduced into a global
context while avoiding conflict with existing namespaces. Use
of naming authorities also allows delegation of service, both
resolution and administration, to a local handle service.
- International Support: The handle namespace is based on Unicode
3.0 [17], which includes most of the characters currently used
around the world. This allows handles to be used in any native
environment. The handle protocol mandates UTF-8 [5] as the
encoding used for handles.
- Distributed Service Model: The Handle System defines a
hierarchical service model such that any local handle namespace
may be serviced by a corresponding local handle service, by the
global service, or by both. The global service, known as the
Global Handle Registry, can be used to dispatch any handle
service request to the responsible local handle service. The
distributed service model allows replication of any given
service into multiple service sites, and each service site may
further distribute its service into a cluster of individual
servers. (Note that local here refers only to namespace and
administrative concerns. A local handle service could in fact
have many service sites distributed across the Internet.)
- Secured Name Service: The Handle System allows secured name
resolution and administration over the public Internet. The
Handle System protocol defines standard mechanisms for both
client and server authentication, as well as service
authorization. It also provides security options to assure
data integrity and confidentiality.
- Distributed Administration Service: Each handle may define its
own administrator(s) or administrator group(s). Ownership of
each handle is defined in terms of its administrator or
administrator groups. This, combined with the Handle System
authentication protocol, allows any handle to be managed
securely over the public network by its administrator at any
network location.
- Efficient Resolution Service: The handle protocol is designed
to allow highly efficient name resolution performance. To
avoid resolution being affected by computationally costly
administration service, separate service interfaces (i.e.,
server processes and their associated communication ports) for
handle name resolution and administration may be defined by any
handle service.
This document provides an overview of the handle namespace and
service architecture. It also compares the Handle System with other
existing Internet services, protocols, and specifications (e.g., DNS
[2, 3], URLs [4], X.500/LDAP [6,7,8], and URN [9,10]). Details of
the handle system data and service model, as well as its
communication protocol, are specified in separate documents. They
can be found under the Handle System website at
http://www.handle.net.
2. Motivations
Since there are a number of name related projects in the Internet
community, it is worth defining exactly where we believe the Handle
System fits. Unfortunately, that is particularly hard because the
other primary naming schemes either take an abstract services
approach (e.g., URI/URN), or an approach to name resolution absent of
a self-contained framework for reliable yet distributed
administration of the underlying databases (e.g., DNS). This makes
categorizing the Handle System difficult.
The Handle System crosses boundaries. Looked at as a name resolution
system, it might be compared to DNS. If used to implement a URI/URN
namespace, it could be used with any URI/URN scheme. If used for
distributed information updates and administration, it could be
considered a simplified-version of a distributed database system.
It is probably best to view the Handle System as a name-attribute
binding service with a specific protocol for securely creating,
updating, maintaining, and accessing a distributed database. It is
designed to be an enabling service for secured information and
resource sharing over networks such as the public Internet.
Applications of the Handle System could include meta-data services
for digital publications, identity management services for virtual
identities, or any other applications that require resolution and/or
administration of globally unique identifiers.
In the spirit of exploration, the Handle System has been designed to
have high performance for name resolution and to push the boundaries
of distributed access control and administration. Unlike most
conventional systems (even distributed systems) that are designed to
have a relatively small number of broadly empowered administrators,
the Handle System allows extremely fine granularity of administrative
control. It has a unique self-contained administrative framework
that de-couples the ownership of each handle from the system
administrators and allows access control to be defined for each
handle value.
It should be noted, that as with all real systems, the Handle System
is a compromise between a number of technical and practical concerns.
There are also different opinions within the IETF on where the Handle
System fits in relation to other existing Internet name services. It
is with the goal of exposing a broader community to the concepts,
approach, specific decisions, tradeoffs and results that we are
writing this RFC.
3. Handle Namespace
Every handle consists of two parts: its naming authority, otherwise
known as its prefix, and a unique local name under the naming
authority, otherwise known as its suffix:
<Handle> ::= <Handle Naming Authority> "/" <Handle Local Name>
The naming authority and local name are separated by the ASCII
character "/". The collection of local names under a naming
authority defines the local handle namespace for that naming
authority. Any local name must be unique under its local namespace.
The uniqueness of a naming authority and a local name under that
authority ensures that any handle is globally unique within the
context of the Handle System.
For example, "10.1045/january99-bearman" is a handle for an article
published in D-Lib magazine [12]. Its naming authority is "10.1045"
and its local name is "january99-bearman". The handle namespace can
be considered a superset of many local namespaces, with each local
namespace having a unique naming authority under the Handle System.
The naming authority identifies the administrative unit of creation,
although not necessarily continuing administration, of the associated
handles. Each naming authority is guaranteed to be globally unique
within the Handle System. Any existing local namespace can join the
global handle namespace by obtaining a unique naming authority so
that any local name under the namespace can be globally referenced as
a combination of the naming authority and the local name as shown
above.
Naming authorities under the Handle System are defined in a
hierarchical fashion resembling a tree structure. Each node and leaf
of the tree is given a label that corresponds to a naming authority
segment. The parent node notifies the parent naming authority of its
child nodes. Unlike DNS, handle naming authorities are constructed
left to right, concatenating the labels from the root of the tree to
the node that represents the naming authority. Each label is
separated by the octet used for ASCII character "." (0x2E). For
example, a naming authority for the National Digital Library Program
("ndlp") at the Library of Congress ("loc") is defined as "loc.ndlp".
Each naming authority may have many child naming authorities
registered underneath. Any child naming authority can only be
registered by its parent after its parent naming authority has been
registered. However, there is no intrinsic administrative
relationship between the namespaces represented by the parent and
child naming authorities. The parent namespace and its child
namespaces may be served by different handle services, and they may
or may not share any administration privileges.
Handles may consist of any printable characters from the Universal
Character Set (UCS-2) of ISO/IEC 10646, which is the exact character
set defined by Unicode v3.0 [17]. The UCS-2 character set
encompasses most characters used in every major language written
today. To allow compatibility with most of the existing systems and
to prevent ambiguity among different encodings, the Handle System
protocol mandates UTF-8 to be the only encoding used for handles.
The UTF-8 encoding preserves any ASCII encoded names so as to allow
maximum compatibility with existing systems without causing naming
conflict. Some encoding issues over the global namespace and the
choice of UTF-8 encoding are discussed in [13].
By default, handles are case sensitive. However, any individual
handle service may define its namespace such that ASCII characters
within any handle under that namespace are case insensitive.
4. Handle System Architecture
The Handle System defines a hierarchical service model. The top
level consists of a single handle service, known as the Global Handle
Registry (GHR). The lower level consists of all other handle
services, generically known as Local Handle Services (LHS).
The Global Handle Registry can be used to manage any handle
namespace. It is unique among handle services only in that it
provides the service used to manage naming authorities, all of which
are managed as handles. The naming authority handle provides
information that clients can use to access and utilize the local
handle service for handles under the naming authority.
Local Handle Services are intended to be hosted by organizations with
administrative responsibility for handles under certain naming
authorities. A Local Handle Service may be responsible for any
number of local handle namespaces, each identified by a unique naming
authority. The Local Handle Service and its responsible set of local
handle namespaces must be registered with the Global Handle Registry.
One important aspect of the Handle System is its distributed
architecture. The Handle System as a whole consists of a number of
individual handle services. Each of these services may consist of
one or more service sites. Each service site is a complete
replication of every other site in the service in terms of handle
resolution. Each service site may consist of one or more handle
servers. All handles, and hence all handle requests, directed at a
given service site will be evenly distributed across these handle
servers. The Handle System as a whole may consist of any number of
handle services. There are no design limits on the number of handle
services or on the number of sites which make up each service, nor
are there any limits on the number of servers that make up each site.
Replication among any service site does not require that each site
contain the same number of servers. In other words, while each site
will have the same replicated set of handles, each site may allocate
that set of handles across a different number of servers. This
distributed approach is intended to aid scalability, accommodate any
large-scale of operation, and mitigate problems of single point
failure.
Figure 3.1 illustrates a potential handle service that consists of
two service sites: one located on the U.S. east coast and the other
on the U.S. west coast. The east coast service site consists of four
server computers. The west coast service site, with more powerful
computers deployed, decides two servers will suffice. The number of
service sites for any handle service, as well as the number of
servers that are used by any service site, may be added or removed
dynamically depending on the service requirement.
------------------------- ------------------
| --------- --------- | | ----- ----- |
| | | | | | | | S | | S | |
| | server1 | | server2 | | | | E | | E | |
| | | | | | | | R | | R | |
| --------- --------- | | | V | | V | |
| --------- --------- | | | E | | E | |
| | | | | | | | R | | R | |
| | Server3 | | Server4 | | | | | | | |
| | | | | | | | 1 | | 2 | |
| --------- --------- | | ----- ----- |
------------------------- ------------------
Handle Service Site 1 Handle Service Site 2
(US East Coast) (US West Coast)
Figure 3.1: Handle service configured with two service sites
Each handle service manages a distinct sub-namespace under the Handle
System. Namespaces under different handle services may not overlap.
The sub-namespace typically consists of handles under a number of
naming authorities. The handle service is called the "home" service
of these naming authorities and is the only one that provides
resolution and administration service for handles under these naming
authorities. Before resolving a handle, a client has to determine
the "home" service of the handle in question. The "home" service of
each handle is the "home" service of its naming authority and is
registered at the Global Handle Registry. Clients can find the
"home" service for each handle by querying the naming authority
handle at the Global Handle Registry.
The Global Handle Registry maintains naming authority handles. Each
naming authority handle maintains the service information that
describes the "home" service of the naming authority. The service
information lists the service sites of the given handle service, as
well as the interface to each handle server within each site. To
find the "home" service for any handle, a client can query the Global
Handle Registry for the service information associated with the
corresponding naming authority handle. The service information
provides the necessary information for clients to communicate with
the "home" service.
Figure 3.2 shows an example of a typical handle resolution process.
In this case, the "home" service is a Local Handle Service. The
client is trying to resolve the handle "10.1045/july95-arms" and has
to find its "home" service from the Global Handle Registry. The
"home" service can be found by sending a query to the Global Handle
Registry for the naming authority handle for "10.1045". The Global
Handle Registry returns the service information of the Local Handle
Service that is responsible for handles under the naming authority
"10.1045". The service information allows the client to communicate
with the Local Handle Service to resolve the handle "10.1045/july95-
arms".
------------------------
| | 4. Result of client request
| Client with global | <-------------------------------.
| service information | |
| | ----------------------------. |
------------------------ 3. Request to responsible | |
| ^ Local Handle Service | |
1. Client | | | |
query for | | | |
naming | | 2. Service information | |
authority | | for "10.1045" V |
"10.1045" | | ----------------------
| | | |
V | | Local Handle Service |
--------------- | responsible for the |
| | | naming authority |
| Global Handle | | "10.1045" |
| Registry | | |
| | ----------------------
---------------
Figure 3.2: Handle resolution starting with global
To improve resolution performance, any client may choose to cache the
service information returned from the Global Handle Registry and use
it for subsequent queries. A separate handle caching server, either
stand-alone or as a piece of a general caching mechanism, may also be
used to provide shared caching within a local community. Given a
cached resolution result, subsequent queries of the same handle may
be answered locally without contacting any handle service. Given
cached service information, clients can send their requests directly
to the correct Local Handle Service without contacting the Global
Handle Registry.
5. Handle System Security
The Handle System provides handle resolution and administration
service over networks such as the public Internet. Each handle can
be assigned a set of values. Clients use the handle resolution
service to resolve any handle into its set of values. Each value has
a data type and a unique value index. Clients can query for specific
handle values based on data type or value index.
The handle administration service answers requests from clients to
manage handles. These include adding handles, deleting handles or
updating their values. It also manages naming authorities via naming
authority handles. Each handle can have its own administrator(s),
and each administrator can be granted a certain set of permissions.
The handle system authentication protocol authenticates the handle
administrator before fulfilling any administrative request.
The Handle System provides security services such as client and
server authentication, data confidentiality and integrity, and non-
repudiation. By default, handle resolution does not require any
client authentication. However, resolution requests for confidential
data assigned to any handle (by its administrator), as well as any
administration requests (e.g., adding or deleting handle values)
require authentication of the client for proper authorization. The
server will decide, during the authorization process, whether or not
the client has permission to access those confidential handle values,
or has permission to add or update handles and handle values. When
authentication is required, the handle server will issue a challenge
to the requesting client before carrying out the client's request.
To satisfy the authentication requirement, the client must send back
the correct response identifying itself as a qualified administrator.
The handle server will respond to the initial request only after
successful authentication of the client. Handle clients may choose
to use either secret key or public key cryptography for
authentication. Handle System authentication can also be carried out
via third party authentication services. To ensure data integrity,
clients may request digitally signed responses from any handle
server. They may also set up secured communication sessions with
handle servers so that any exchanged information can be encrypted
(for data confidentiality) using a session key. Handle servers can
also provide confidentiality by encrypting the handle data before
sending it to the client.
The Handle System provides service options for secured information
exchange between the client and server. This does not, of course,
guarantee the truthfulness of handle values. Incorrect values
assigned to any handle by its administrator may very well mislead
clients. On the other hand, a handle value may contain references to
other handle values to provide additional credentials. For example,
a handle value R (e.g., a claim) may contain a reference to some
other handle value that contains the digital signature (from a
creditable source) upon the value R. Clients who trust the signature
could then trust the handle value R.
6. The Handle System and other Internet Services
There are a number of existing and proposed Internet identifier
services or specifications that, by design or intent, cover some of
the functionalities proposed for the Handle System. This section
briefly reviews them in relationship to the Handle System.
6.1. Domain Name Service (DNS)
The Domain Name Service, or DNS, was originally designed and is
heavily used for mapping domain names into IP Addresses for network
routing purposes. RFC 1034 [2] and RFC 1035 [3] provide detailed
descriptions of its design and implementation. The growth of the
Internet has increased demands for various extensions to DNS, even
its possible use as a general purpose resource naming system.
However, any such use has the potential to slow down the network
address translation and/or affect its effectiveness in network
routing. DNS implementations typically do not scale well when a
large amount of data is associated with any particular DNS name. It
is therefore generally considered inappropriate to use DNS as a
general-purpose naming service.
An additional factor that argues against using DNS as a general-
purpose naming service is the DNS administrative model. DNS names
are typically managed by the network administrator(s) at the DNS zone
level. There is no provision for a per-name administrative
structure. No facilities are provided for anyone other than network
administrators to create or manage DNS names. This is appropriate
for domain name administration but less so for general-purpose name
administration.
The Handle System differs from DNS in its distributed administration
and service model, as well as its security features. The handle
system protocol includes security options to assure confidentiality
and integrity during data transmission. Each handle can have its own
administrator, independent from the server administrator. The handle
system protocol allows any handle administrator to manage his or her
handles securely over the public network. Additionally, the Handle
System service model allows any of its service sites to dynamically
configure its service distribution among a cluster of servers to
accommodate increased service requests. This also allows less
powerful computers to be used together to support any arbitrarily
large number of handles.
6.2. Directory Services (X.500/LDAP)
X.500 [6] is the OSI Directory Standard defined by the ISO and the
ITU. It is designed "to provide a white pages service that would
return either the telephone numbers or X.400 O/R addresses of
people", and is "concerned mainly with providing the name server
service for Open Systems Interconnection (OSI) applications" [7].
X.500 defines a hierarchical data and information model with a set of
protocols to allow global name lookup and search. The protocol,
however, has proved difficult to implement and there has been
difficulty in getting "client access integrated into existing
products" [14]. LDAP (Lightweight Directory Access Protocol) [8] has
overcome many of these difficulties by making the protocol simpler
and easier to implement. Some concern remains, however, that as LDAP
is emerging from a local directory access protocol (LDAP v2) into a
distributed service protocol (LDAP v3), it faces many issues not
addressed in its original design, resulting in new complications.
The fundamental difference between a name resolution service such as
the Handle System, and a directory service such as LDAP, is search
capability. The added functionality of being able to search a
directory service necessarily carries with it added complexity, thus
affects its efficiency. A pure name service, such as the Handle
System, can be designed solely around efficient resolution of known
items without addressing functions and data structures required for
discovery of unknown items based on incomplete criteria.
Directory services, such as LDAP or WHOIS++ [15,16], may be used in
tandem with the Handle System to provide reverse lookup service.
Existing corporate directory services, for example, could provide
interfaces to both services. The Handle System interface would
provide a highly efficient name resolution service. The directory
service interface would provide extended search capability. Handles
could also be used in LDAP service referral. For example, an LDAP
service may be referenced as a handle. Doing so will make the
reference persistent overtime, independent of location change.
6.3. Uniform Resource Identifier (URI)/Uniform Resource Name(URN)
Uniform Resource Identifier (URI) [23] defines a uniform, yet
extensible naming mechanism for identifying Internet resources in web
applications. Uniform Resource Name (URN) [11], a subset of URI,
defines a namespace registration mechanism for persistent namespaces
under URI. URI/URN represents most of the Internet name services
used in web applications. This section discusses the relationship of
the Handle System to URI/URN and how applications may utilize the
Handle System within the URI/URN context.
The Handle System provides a general-purpose name service for the
Internet. Like DNS or X.500 directory service, the Handle System
defines its namespace outside of any URI/URN namespace. Handles can
be transcribed and resolved directly, without any URI/URN scheme as a
prefix. For example, a library application may resolve the handle
"10.1045/july95-arms" directly into its set of handle values. No
URI/URN scheme will be needed in this case.
The Handle System may be used for applications that require a
persistent name service. The Handle System provides the necessary
mechanisms to allow persistent names to be registered as handles.
Specific naming authorities may be defined to host those handles
designed to be persistent. However, the persistence of handles
depends more on administrative policies than the technology itself.
Such policies are beyond the Handle System service, as described in
this set of documents.
On the other hand, the Handle System can also be used for
applications where persistent names are not required. Such handles
may have a short life-time and they may also be used to identify
different objects at different times.
Different web applications may be developed using the Handle System
as the underlying name service. Each of these applications may
define its own URI/URN namespace for its application needs. For
example, application FOO may have a URI namespace "foo:" registered
to identify any FOO services on the web. In the mean time,
application BAR may have a URN namespace "URN:BAR" registered to
identify any BAR object that needs a persistent name. Both FOO and
BAR applications may use handles (under their respective naming
authority) in naming and resolving to services and/or objects. This
is similar in DNS, where there are different URI schemes (e.g.,
"telnet", "ftp", "mailto", etc.) defined for different applications,
all using the DNS service.
The IETF and IRTF have discussed the Handle System in the realm of
URI-related work. There are different opinions on whether the Handle
System will fit into a specific URI or URN namespace. There are also
concerns on where the Handle System fits in relation to other
existing name services on the Internet. Such discussions are out of
the scope of this document.
7. Security Considerations
This section is meant to inform people of security limitations of the
Handle System, as well as precautions that should be taken by
application developers, service providers, and Handle System clients.
Specific security considerations regarding the Handle System protocol
[21], as well as its data and service model [22], are addressed in
separate documents.
7.1. General Security Practice
The security of the Handle System depends on both client and server
host security at every step in the transaction. It assumes the
client host has not been tampered with and that client software will
reliably convey the received data to the client. The client of any
handle service must also assume that any handle servers involved have
not been compromised. To trust the Global Handle Registry is to
believe that the Global Handle Registry will correctly direct the
client request to the responsible Local Handle Service. To trust a
Local Handle Service is to believe that the Local Handle Service will
correctly return the data that was assigned to the handle by its
administrator. A Local Handle Service typically supports a set of
naming authorities. Thus, trusting a Local Handle Service would
imply trusting those naming authorities.
The integrity of the Handle System depends heavily on the integrity
of the global service information. Invalid global service
information may mislead clients into inappropriate Local Handle
Services. It may also allow attackers to forge server signatures.
The Global Handle Registry must take extreme caution in protecting
the global service information and the public key pair used to sign
the global service information. Client applications should only
accept the global service information from the Global Handle
Registry. They should check its integrity upon each update.
For efficiency reasons, handle servers will not generate or return a
digital signature for every service response, unless specifically
requested by clients. To assure data integrity, clients must
explicitly ask the server to return the digital signature. To
protect sensitive data from exposure, clients may establish a
communication session with the server and ask the server to encrypt
any data using the session key.
7.2. Privacy Protection
By default, most handle data stored in the Handle System is publicly
accessible, unless otherwise specified by the handle administrator.
Handle administrators must pay attention when adding handle values
that contain private information. They may choose to mark these
handle values readable only by the handle administrator(s), or to
store these as encrypted handle values, so that these values can only
be read within a controlled audience.
Log files generated by the handle server are another vulnerable point
where client privacy may be under attack. Operators of handle
servers must protect such information carefully.
7.3. Caching and Proxy Servers
Besides performance gains and other value-added services, both proxy
and caching servers present themselves as men-in-the-middle, and as
such are vulnerable to man-in-the-middle attacks. It is important to
know that proxy and caching servers are not part of any handle
service. They are clients of the Handle System. Service responses
from proxy and caching servers cannot be authenticated via the Handle
System protocol. The trust between the client and its immediate
proxy/caching server has to be setup independently, regardless of the
number of proxy/caching servers that are in the middle of the
communication path.
By using proxy and caching servers, clients assume that the servers
will submit their requests and relay any responses from the Handle
System without mishandling any of the contents. They also assume
that the servers will protect any sensitive information on their
behalf.
Proxy and caching server operators should protect the systems on
which such servers are running as they would protect any system that
contains or transports sensitive information. In particular, log
information gathered at proxies often contain highly sensitive
personal information, and/or information about organizations. Such
information should be carefully guarded, and appropriate guidelines
for their use developed and followed.
Caching servers provide additional potential vulnerabilities because
the contents of the cache represent an attractive target for
malicious exploitation. Potential attacks on the cache can reveal
private data for a handle user, or information still kept after a
user believes that they have been removed from the network.
Therefore, cache contents should be protected as sensitive
information.
7.4. Mirroring
Handle System clients should be aware of possible delays in content
replication among mirroring sites. They should consider sending
their request to the primary service site for any time-sensitive
data. Selection of mirroring sites by service administrators must be
done carefully. Each mirroring site must follow the same security
procedures in order to ensure data integrity. Software tools may be
applied to ensure data consistency among mirroring sites.
7.5. Denial of Service (DoS)
As with any public service, the Handle System is subject to denial of
service attacks. No general solutions are available to protect
against such attacks in today's technology. Server implementations
may be developed to be aware of such attacks and notify
administrators when they happen. Stateless cookies [19, 20] are one
means of mitigating some of the effects of DoS attacks on hosts that
perform authentication, integrity, and encryption services. Server
implementations, moreover, need to be upgradeable to take advantage
of new security technologies, including anti-DoS technologies as
these become available.
8. History of the Handle System
The Handle System was originally conceived and developed at CNRI as
part of an overall digital object architecture. The first public
implementation was created at CNRI in the fall of 1994 in an effort
led by David Ely. The overall digital object architecture, including
the Handle System, was later described in a paper by Robert Kahn and
Robert Wilensky [1] in 1995. Development continued at CNRI as part
of the Computer Science Technical Reports (CSTR) project, funded by
the Defense Advanced Projects Agency (DARPA) under Grant Number MDA-
972-92-J-1029 and MDA-972-99-1-0018. One aspect of this early
digital library project, which was also a major factor in the
evolution of the Networked Computer Science Technical Reference
Library (NCSTRL) [18] and related activities, was to develop a
framework for the underlying infrastructure of digital libraries.
Early adopters of the Handle System included the Library of Congress,
the Defense Technical Information Center (DTIC), and the
International DOI Foundation (IDF). Feedback from these
organizations as well as NCSTRL, other digital library projects, and
related IETF efforts as mentioned above, have all contributed to the
evolution of the Handle System. The current status and available
software, for both client and server, can be found at
http://www.handle.net.
9. Acknowledgements
This work is derived from the earlier versions of the Handle System
implementation. Design ideas are based on those discussed within the
Handle System development team, including David Ely, Charles Orth,
Allison Yu, Sean Reilly, Jane Euler, Catherine Rey, Stephanie Nguyen,
Jason Petrone, and Helen She. Their contributions to this work are
gratefully acknowledged.
The authors also thank Russ Housley (housley@vigilsec.com), Ted
Hardie (hardie@qualcomm.com), and Mark Baugher (mbaugher@cisco.com)
for their extensive review and comments, as well as recommendations
received from other members of the IETF/IRTF community.
10. References and Bibliography
[1] Kahn, R. and R. Wilensky, "A Framework for Distributed Digital
Object Services", D-Lib Magazine, 1995.
[2] Mockapetris, P., "Domain Names - Concepts and Facilities", STD
13, RFC 1034, November 1987.
[3] Mockapetris, P., "Domain Names - Implementation and
Specification", STD 13, RFC 1035, November 1987.
[4] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
Locators (URL)", RFC 1738, December 1994.
[5] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
10646", RFC 2044, October 1996.
[6] ITU-T Rec. X.500, "The Directory: Overview of Concepts, Models,
and Services", 1993.
[7] D. W. Chadwick, "Understanding X.500 - The Directory", Chapman &
Hall ISBN: 0-412-43020-7.
[8] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[9] Sollins, K. and L. Masinter, "Functional Requirements for
Uniform Resource Names", RFC 1737, December 1994.
[10] Sollins, K. "Architectural Principles of Uniform Resource Name
Resolution", RFC 2276, January 1998.
[11] IETF Uniform Resource Names (URN) Working Group, April 1998.
[12] D-Lib Magazine, http://www.dlib.org
[13] Sam X. Sun, "Internationalization of the Handle System - A
Persistent Global Name Service", Proceeding of 12th
International Unicode Conference, April 1998.
[14] D. Goodman, C. Robbins, "Understanding LDAP & X.500", August
1997.
[15] Deutsch P., Schoultz R., Faltstrom P. and C. Weider,
"Architecture of the WHOIS++ service", RFC 1835, August 1995.
[16] Weider, C., Fullton, J. and S. Spero, "Architecture of the
Whois++ Index Service", RFC 1913, February 1996.
[17] The Unicode Consortium, "The Unicode Standard, Version v3.0",
Addison-Wesley Pub Co; ISBN: 0201616335.
[18] The Networked Computer Science Technical Reports Library
(NCSTRL), http://www.ncstrl.org/
[19] Karn, P. and W. Simpson, "Photuris: Session-Key Management
Protocol", RFC 2522, March 1999.
[20] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[21] Sun, S., Reilly, S. and L. Lannom, "Handle System Namespace and
Service Definition", RFC 3651, November 2003.
[22] Sun, S., Reilly, S., Lannom, L. and J. Petrone, "Handle System
Protocol (ver 2.1) Specification", RFC 3652, November 2003.
[23] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
11. Authors' Addresses
Sam X. Sun
Corporation for National Research Initiatives (CNRI)
1895 Preston White Dr., Suite 100
Reston, VA 20191
Phone: 703-262-5316
EMail: ssun@cnri.reston.va.us
Larry Lannom
Corporation for National Research Initiatives (CNRI)
1895 Preston White Dr., Suite 100
Reston, VA 20191
Phone: 703-620-8990
EMail: llannom@cnri.reston.va.us
Brian Boesch
Corporation for National Research Initiatives (CNRI)
1895 Preston White Dr., Suite 100
Reston, VA 20191
Phone: 703-262-5316
EMail: bboesch@cnri.reston.va.us
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